Remove m_OneUse requirement only for max, not min

If it is ever determined that min doesn't need one-use, then we can in fact remove that version entirely.
llvm · Feb 22, 2024 · 5a8264c · 5a8264c
1 parent ae3e142
commit 5a8264c
Show file tree

Hide file tree

Showing 3 changed files with 23 additions and 9 deletions.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2277,14 +2277,28 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
 
     // max X, -X --> fabs X
     // min X, -X --> -(fabs X)
-    // TODO: Remove one-use limitation? That is obviously better for max.
-    //       It would be an extra instruction for min (fnabs), but that is
-    //       still likely better for analysis and codegen.
-    if ((match(Arg0, m_OneUse(m_FNeg(m_Value(X)))) && Arg1 == X) ||
-        (match(Arg1, m_OneUse(m_FNeg(m_Value(X)))) && Arg0 == X)) {
+
+    // No one-use. Only for max.
+    // TODO: Remove one-use limitation? That is obviously better for max,
+    // hence why we don't check for one-use for that. However,
+    // it would be an extra instruction for min (fnabs), but
+    // that is still likely better for analysis and codegen.
+    // If so, then allow this if-statement clause to handle min,
+    // and delete the clause below this one.
+    if ((((match(Arg0, m_FNeg(m_Value(X)))) && match(Arg1, m_Specific(X))) ||
+         (match(Arg1, m_FNeg(m_Value(X))) && match(Arg0, m_Specific(X)))) &&
+        IID != Intrinsic::minimum && IID != Intrinsic::minnum) {
+      Value *R = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, II);
+      return replaceInstUsesWith(*II, R);
+    }
+
+    // One-use version for min.
+    if ((match(Arg0, m_OneUse(m_FNeg(m_Value(X)))) &&
+         match(Arg1, m_Specific(X))) ||
+        (match(Arg1, m_OneUse(m_FNeg(m_Value(X)))) &&
+         match(Arg0, m_Specific(X)))) {
       Value *R = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, II);
-      if (IID == Intrinsic::minimum || IID == Intrinsic::minnum)
-        R = Builder.CreateFNegFMF(R, II);
+      R = Builder.CreateFNegFMF(R, II);
       return replaceInstUsesWith(*II, R);
     }
 

diff --git a/llvm/test/Transforms/InstCombine/maximum.ll b/llvm/test/Transforms/InstCombine/maximum.ll
@@ -436,7 +436,7 @@ define float @negated_op_extra_use(float %x) {
 ; CHECK-LABEL: @negated_op_extra_use(
 ; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEGX]])
-; CHECK-NEXT:    [[R:%.*]] = call float @llvm.maximum.f32(float [[NEGX]], float [[X]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %negx = fneg float %x

diff --git a/llvm/test/Transforms/InstCombine/maxnum.ll b/llvm/test/Transforms/InstCombine/maxnum.ll
@@ -458,7 +458,7 @@ define float @negated_op_extra_use(float %x) {
 ; CHECK-LABEL: @negated_op_extra_use(
 ; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEGX]])
-; CHECK-NEXT:    [[R:%.*]] = call float @llvm.maxnum.f32(float [[NEGX]], float [[X]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %negx = fneg float %x